Scheduling mechanism for MAC entity

ABSTRACT

A code division multiple access (CDMA) radio network controller (RNC) comprises a medium access controller-controlling/shared (MAC-c/sh) entity. The MAC-c/sh entity has a scheduling mechanism managing a forward access channel (FACH) resources. The scheduling mechanism schedules data for transfer over the FACH according to priority of the data and the data having an indicator of a priority of the data.

CROSS REFERENCE TO RELATED APPLICATION(S)

[0001] This application is a continuation of U.S. patent applicationSer. No. 09/569,731, filed May 12, 2000, which is incorporated byreference as if fully set forth.

BACKGROUND

[0002] The invention generally relates to channels used by multipleusers in a wireless code division multiple access spread spectrumsystem. More specifically, the invention relates to a system and methodof prioritizing and controlling the flow of data for common and sharedchannels in a spread spectrum system.

[0003]FIG. 1 illustrates a simplified wireless spread spectrum codedivision multiple access (CDMA) communication system 18. A node b 26within the system 18 communicates with associated user equipment 20-24(UE). The node b 26 has a single site controller (SC) 30 associated witheither a single (shown in FIG. 1) or multiple base stations 28. A Groupof node bs 26, 32, 34 is connected to a radio network controller (RNC)36. To transfer communications between RNCs 36-40, an interface betweenthe RNCs (IUR) 42 is utilized. Each RNC 36-40 is connected to a mobileswitching center (MSC) 44 which in turn is connected to the core network46.

[0004] To communicate within the system 18, many types of communicationchannels are used, such as dedicated, shared and common. Dedicatedchannels transfer data between a node b 26 and a particular UE 20-24.Common and shared channels are used by multiple UEs 20-24 or users. Allof these channels carry a variety of data including traffic, control andsignaling data.

[0005] Since shared and common channels carry data for different users,data is sent using protocol data units (PDUs) or packets. As shown inFIG. 2, to regulate the flow of data from differing sources 48-52 into achannel 56, a controller 54 is used.

[0006] One common channel used for transmitting data to the UEs 20-24 isthe forward access common channel (FACH) 58. As shown in FIG. 3, theFACH 58 originates in a RNC 36 and is sent to a node b 28-34 forwireless transmission as a spread spectrum signal to the UEs 20-24. TheFACH 58 carriers several data types from various sources, such as acommon control channel (CCCH), dedicated control and traffic channel(DCCH and DTCH), and a downlink and uplink share channel (DSCH and USCH)control signaling. The FACH 58 also carries control signaling out ofband, such as hybrid automatic repeat request (H-ARQ), and similar datatransmitted via the IUR 62 from other RNCs 38-40, such as CCCH, DCCH,DTCH and H-ARQ control data.

[0007] Various controllers are used by the RNC 36 to control the flow ofdata. A radio link controller (RLC) 64 handles the CCCH. The dedicatedmedium access controller (MAC-d) 66 handles the DCCH, the DTCH and someout of band H-ARQ signaling. The shared medium access controller(MAC-sh) 68 handles the DSCH, USCH control signaling and out of bandH-ARQ control signaling. Controlling the FACH 58 is the common mediumaccess controller (MAC-c) 60.

[0008] Due to the multiple sources of data 48-52 that can be transmittedover a common or shared channel, the channel controllers 54 queue thedata prior to transmission. If a large backlog develops in the queue,data in the queue develops a latency. A large latency of certain datasuch as control data will result in the failure of a channel. Toalleviate this problem, the prior art either flushed the queue to reducecongestion or rerouted the data. Flushing the queue results in the lossof data and requires retransmission which is undesirable. Rerouting dataalready queued creates a duplication of data within the system and doesnot resolve the existing congestion. According, it is desirable toreduce the latency of data for shared and common channels without theproblems associated with the prior art.

SUMMARY

[0009] A code division multiple access (CDMA) radio network controller(RNC) comprises a medium access controller-controlling/shared (MAC-c/sh)entity. The MAC-c/sh entity has a scheduling mechanism managing aforward access channel (FACH) resources. The scheduling mechanismschedules data for transfer over the FACH according to priority of thedata and the data having an indicator of a priority of the data.

BRIEF DESCRIPTION OF THE DRAWING(S)

[0010]FIG. 1 is a simplified illustration of a wireless spread spectrumcommunication system.

[0011]FIG. 2 is an illustration of data flowing into a common or sharedchannel.

[0012]FIG. 3 is an illustration of data flowing into a FACH channelwithin a RNC.

[0013]FIG. 4 is an illustration of a prioritization scheme.

[0014]FIG. 5 is a prioritization scheme for use with a FACH channel.

[0015]FIG. 6 depicts a reservation mechanism used with a common orshared channel.

[0016]FIG. 7 depicts data source windows used with a common or sharedchannel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

[0017] Data prioritization 70 is used to reduce data latency in amultiuser channel controller 54 as illustrated in FIG. 4. For aparticular common or shared channel, certain data must be transmitted onthat channel and is shown in the figure as “mandatory” 88. Other data ispreferably sent on the particular channel but may be rerouted to anotherchannel, such as a dedicated channel. This data is referred to as “besteffort” 90. Since “mandatory” data 88 is not reroutable, it takespriority over “best effort” data 90.

[0018] The type of the data within a packet, such as control 96,signaling 98 and traffic data 100, is also used for prioritization. Toaccomplish prioritization of the data type, control 96 and signaling 98data packets are separated from traffic data packets 100. One approachto separating the packets is to group similar data type packets togetherprior to reception at the controller 54. Alternately, packets sent byeach channel prior to reception by the controller 54 are provided with aflag or identifier indicating the packets' data type.

[0019] Since a prolonged delay in the transfer of control 96 orsignaling 98 data results in a frozen channel, control 96 and signaling98 data are given a higher priority than traffic data 100. Additionally,data associated with multiple users, common or shared 92, has a higherpriority than data for a single user, dedicated 94. The dataprioritization scheme is typically stored in the software of themultiuser channel's controller.

[0020] During periods of high congestion, data is rerouted to otherchannels based on its priority 70. For instance, best effort dedicatedtraffic data is rerouted and mandatory common control data is not. Byrerouting data prior to queuing, retransmissions will not be required.Accordingly, the amount of queued data is reduced resulting in lowerdata latency. Additionally, since the rerouted data is never queued, theduplication of data as experienced in the prior art is eliminated.

[0021] A prioritization scheme 72 for use with a FACH 58 is shown inFIG. 5. Since the DSCH, H-ARQ of the MAC-sh have mandatory sharedcontrol data, they have the highest priority, highest. Although theH-ARQ of the MAC-d has mandatory control data, being dedicated it isassigned a slightly lower priority, high. The CCCH and DCCH are used forsignaling and have the next level of priority, medium. The lowest levelof priority is assigned to the DTCH because it has best effort dedicatedtraffic data.

[0022] To facilitate this prioritization scheme 72 for the FACH 58,modifications to the RNC 36 are required. As shown in FIG. 3, the priorart MAC-d 66 controls the DCCH, DTCH and MAC-d's H-ARQ. As shown in FIG.5, each of these sources has a different priority. Since this data ismultiplexed prior to prioritization at the MAC-d 66, the multiplexer ofthe MAC-d 66 is moved to the MAC-c 60 to allow prioritization at theMAC-c 60. Alternatively, the MAC-d 66 may send the priority and class(mandatory or best effort), such as by a flag or identifier, of eachpacket of the multiplexed data for prioritization at the MAC-c 60. Thedata controlled by the RLC 64 and the MAC-sh 68 have equal priority andaccordingly, neither requires modification. Using the stored prioritylist, the data from the various sources is scheduled for transmissionand rerouted during periods of high congestion.

[0023] Another technique for reducing the latency of data which may becombined with prioritization is to control the flow of data between thevarious controllers. As shown in FIG. 6, a scheduling mechanism 74 isused to regulate the data entering the common or shared channel 56. Thescheduling mechanism 74 tracks the backlog of data in the controller'squeue. If the mechanism 74 recognizes congestion and that the data willnot be transmitted in a certain period of time, access to the channel 56limits the flow of data from the individual data sources. The individualsources will recognize the need to reroute data or to not attempttransmission. Using a flow control mechanism with a FACH, MAC and RLC(Layer 2), the latency of signaling is decreased thus increasingefficiency.

[0024] To prevent the monopolization of the common or shared channel 56by one data source 48-52 variable windows 76-86 may be used as shown inFIG. 7. Each data source 48-52 has a window or multiple windows 76-86 ofoutstanding data in the queue that it is permitted. The size of thewindow 76 is based on the requirements of the specific source. Thewindow 76 is dynamically adjusted in response to the availability of thequeue. As the availability of the channel increases, the size of thewindows increases which increases the number of outstanding packets.Conversely, as the availability decreases, the size of the windowsdecreases which decreases the number of outstanding packets. As a resultof the decreased windows, the data sources either reroute or stopsending packets to the windows.

What is claimed is:
 1. A code division multiple access (CDMA) radionetwork controller (RNC) comprising: a medium accesscontroller—controlling/shared (MAC-c/sh) entity having a schedulingmechanism, the scheduling mechanism manages a forward access commonchannel (FACH) resources, the scheduling mechanism schedules data fortransfer over the FACH according to a priority of the data and the datahaving an indicator of a priority of the data.
 2. The CDMA RNC of claim1 wherein the MAC-c/sh entity limiting data transferred over the FACH.3. The CDMA RNC of claim 2 wherein the limiting is associated with asource of the data.
 4. The CDMA RNC of claim 3 wherein the limiting of aparticular source is by controlling a size of a window associated withthe source.